STEER/AliKFVertex.cxx

   1 //----------------------------------------------------------------------------
   2 // Implementation of the AliKFVertex class
   3 // .
   4 // @author  S.Gorbunov, I.Kisel
   5 // @version 1.0
   6 // @since   13.05.07
   7 //
   8 // Class to reconstruct and store primary and secondary vertices
   9 // The method is described in CBM-SOFT note 2007-003,
  10 // ``Reconstruction of decayed particles based on the Kalman filter'',
  11 // http://www.gsi.de/documents/DOC-2007-May-14-1.pdf
  12 //
  13 // This class is ALICE interface to general mathematics in AliKFParticleCore
  14 //
  15 //  -= Copyright &copy ALICE HLT Group =-
  16 //____________________________________________________________________________
  17
  18
  19 #include "AliKFVertex.h"
  20
  21
  22 ClassImp(AliKFVertex)
  23
  24
  25 AliKFVertex::AliKFVertex( const AliESDVertex &vertex )
  26 {
  27   // Constructor from ALICE ESD vertex
  28
  29   vertex.GetXYZ( fP );
  30   vertex.GetCovMatrix( fC );
  31   fChi2 = vertex.GetChi2();
  32   fNDF = 2*vertex.GetNContributors() - 3;
  33   fQ = 0;
  34   fAtProductionVertex = 0;
  35   fIsLinearized = 0;
  36   fSFromDecay = 0;
  37 }
  38
  39
  40 void AliKFVertex::ConstructPrimaryVertex( const AliKFParticle *vDaughters[],
  41                                           int NDaughters, Bool_t vtxFlag[],
  42                                           Double_t ChiCut  )
  43 {
  44   //* Primary vertex finder with simple rejection of outliers
  45   if( NDaughters<2 ) return;
  46   Construct( vDaughters, NDaughters );
  47   for( int i=0; i<NDaughters; i++ ) vtxFlag[i] = 1;
  48
  49   Int_t nRest = NDaughters;
  50   while( nRest>2 )
  51     {
  52       Double_t worstChi = 0.;
  53       Int_t worstDaughter = 0;
  54       for( Int_t it=0; it<NDaughters; it++ ){
  55         if( !vtxFlag[it] ) continue;
  56         const AliKFParticle &p = *(vDaughters[it]);
  57         AliKFVertex tmp = *this - p;
  58         Double_t chi = p.GetDeviationFromVertex( tmp );
  59         if( worstChi < chi ){
  60           worstChi = chi;
  61           worstDaughter = it;
  62         }
  63       }
  64       if( worstChi < ChiCut ) break;
  65
  66       vtxFlag[worstDaughter] = 0;
  67       *this -= *(vDaughters[worstDaughter]);
  68       nRest--;
  69     }
  70
  71   if( nRest<=2 && GetChi2()>ChiCut*ChiCut*GetNDF() ){
  72     for( int i=0; i<NDaughters; i++ ) vtxFlag[i] = 0;
  73     fNDF = -3;
  74     fChi2 = 0;
  75   }
  76 }